1. Field of Invention
This invention concerns leveling and angle measuring devices, apparatus and methods for calibration.
2. Description of Prior Art
Traditional precision machining utilizing turning lathe, drilling and milling machines were typically operated by skilled machinist through precise adjusting each X, Y and Z axis to complete a machining component or part. These skilled-labor dependent machines has been radically replaced by very high precision, augmented machining speed, multiple axis, fully automatic computer numerical control (CNC) machines. These programmable CNC machines are capable of non-stop running in production lines integrated with automatic robotic manipulators for material input and removing the machined part.
Driven by automobile, semiconductor and clean energy of precision engineering industries, the demand for tighter tolerance machining part—higher precision), High speed machining—vibration becomes important issue affecting machine's accuracy, High volume machining and complex machined part—production yield significantly affecting cost and delivery lead time, Larger size of machined part and harder materials, have emerged as critical variables influencing these advanced CNC machines accuracy performance and machine—part production yield requirements.
In contrast, machine leveling and alignment instrument used for manufacturing, installation, set up and maintenance of these advanced CNC machines and metrology equipment remains relatively unchanged. Machinists are still using the traditional single-axis ‘bubble’ spirit level or conventional single-axis digital leveling instrument to perform machine leveling tasks which are unarguably ineffective—time consuming, skilled-operator dependent, and difficult to verify machine leveling status when machine setup activity completed.
Current drawbacks associated with using conventional single-axis leveling devices to align precision machines in attaining positional stability and precise leveled state are as follows:
First, the task confronted by the machine operator for leveling a machine is a two-dimensional planar surface alignment issue. In contrast, traditional leveling and angle measuring instruments are single axis or one directional. Machine leveling operator is required to adjust a machine-frame footings one axis at a time. Since aligning a machine structure involves planar surface, adjusting one axis of the machine affect the other axis of existing plane. Thus, the operator has to do trial-and-error by going back-and-forth in adjusting each footing until the machine surface plane (i.e. where the leveling instrument is placed) is completely leveled. This is a tedious, time consuming and nonproductive task, yet critical affecting machine accuracy and yield performance. The operator could potentially resort to compromise in facing such lengthy repetitive task of iteration.
Second, leveling a machine using traditional spirit level or digital level typically requires two operators. One operator looks at the instrument for current leveling status while the other operator adjusting at the machine footings one at a time. Prolonged iteration to get a machine leveled tends to promote compromised works of the two operators involved and thus increase the risk that the machine is not being optimally leveled to the required specification.
Third, unleveled machine would deform machine structure and affect machine surface plane flatness, cause dimension changes and incur additional machine structural vibration that result in the deterioration of machine accuracy performance. Traditional leveling instruments are not equipped with vibration diagnostic sensors to verify machine leveling positional stability when machine operator alignment task has completed. In particularly, if one footing of a machine is not taking its appropriate weight load during machine setup adjustment (i.e. when machine in static state is just touch on the ground), and when the machine is in operating state (i.e. during machine in dynamic state), induced vibration known as machine ‘rocking’ occurs. Machine structure tends to promote ‘rocking’ when fast-moving machine sub-unit driven by motors (such as milling head), generates inertia and the disposition weight shifts the center of gravity to a different location within the machine causing unstable machine positional stability.
Fourth, conventional angle calibration apparatus employs single-axis rotary plate and is unable to generate simultaneous 2-dimentional surface planar angle. Calibrating one axis at a time subjects the calibration system to inter-axis offset error when calibrating 2-axis angle measuring device. This offset error is the result of the first axis reference position has been displaced when removing the instrument for calibrating the second axis. It also increases calibration time due to multiple set up procedure on reference zero.
Accordingly, improved leveling devices and calibration apparatus are desired that address the forgoing shortcomings of current single-axis leveling devices and calibration apparatus.